Transistors are an integral component in many modern electronic devices. Although used in a variety of applications, many transistors are used as switching devices. Transistors used as switching devices generally require biasing circuitry including an active power supply. The active power supply for biasing the transistors may decrease the battery life of a mobile device, introduce noise into surrounding circuitry, and consume valuable real estate within a device.
FIG. 1 shows a conventional transistor switching device 10. The conventional transistor switching device 10 includes a transistor TR, a gate resistor RG, a body resistor RB, an input port 12, an output port 14, a gate biasing port 16, and a body biasing port 18. In operation, the conventional transistor switching device 10 is maintained in either an on state or an off state. In an off state, the conventional transistor switching device 10 does not pass a signal at the input port 12 to the output port 14. In an on state, the conventional transistor switching device 10 does pass a signal at the input port 12 to the output port 14. In order to maintain the conventional transistor switching device 10 in an off state, the gate biasing port 16 is generally maintained at a voltage lower than that of the body biasing port 18. Accordingly, biasing circuitry including a negative charge pump is often used to maintain a negative potential between the gate biasing port 16 and the body biasing port 18. Similarly, in order to maintain the conventional transistor switching device 10 in an on state, the gate biasing port 16 is generally maintained at a voltage higher than that of the body biasing port 18. Accordingly, biasing circuitry is often used to maintain a positive potential between the gate biasing port 16 and the body biasing port 18. The negative charge pump may reduce the battery life of a device into which it is incorporated, introduce noise into surrounding circuitry, and consume valuable real estate within a device.
In electronic devices dealing with high amplitude signals, multiple switching elements may be coupled together in order to manage the switching of the signal without damage to each one of the switching elements. FIG. 2 shows a conventional shunt switch array 20 comprising a plurality of conventional transistor switching devices TR1-TRN coupled in series between an input node 24 and ground. Bias control circuitry 26 is coupled to each one of the plurality of conventional transistor switching devices TR1-TRN in order to maintain the conventional transistor switching devices in either an on state or an off state. The bias control circuitry 26 may be adapted to generate a biasing voltage VBIAS based upon a received supply voltage VSUPPLY. In order to generate the biasing voltage VBIAS, the bias control circuitry 26 may contain a negative charge pump, a positive charge pump, or both. The negative charge pump and the positive charge pump may reduce the battery life of a device into which they are incorporated, introduce noise into surrounding circuitry, and consume valuable real estate within a device.
FIG. 3 shows a conventional series switch array 28 comprising a plurality of conventional transistor switching devices TR1-TRN coupled in series between an input node 32 and an output node 34. The bias control circuitry 26 is coupled to each one of the plurality of conventional transistor switching devices TR1-TRN in order to maintain the conventional transistor switching devices in either an on state or an off state. The bias control circuitry 26 may be adapted to generate a biasing voltage VBIAS based upon a received supply voltage VSUPPLY. In order to generate the biasing voltage VBIAS, the bias control circuitry 26 may contain a negative charge pump, a positive charge pump, or both. The negative charge pump and the positive charge pump may reduce the battery life of a device into which they are incorporated, introduce noise into surrounding circuitry, and consume valuable real estate within a device.
FIG. 4 shows details of the bias control circuitry 26 shown in FIGS. 2 and 3. As discussed above, the bias control circuitry 26 may include a charge pump 36 in order to generate the biasing voltage VBIAS. The charge pump 36 may be adapted to generate the biasing voltage VBIAS based on the supply voltage VSUPPLY. As shown in FIG. 4, the charge pump 36 may comprise a flying capacitor CFLY1 including a first terminal 38A and a second terminal 38B, a first charge pump switch SWCP1, a second charge pump switch SWCP2, a third charge pump switch SWCP3, a fourth charge pump switch SWCP4, and a clock generator 40.
The first charge pump switch SWCP1 may be adapted to selectively couple the first terminal 38A of the flying capacitor CFLY to the supply voltage VSUPPLY. The second charge pump switch SWCP2 may be adapted to selectively couple the first terminal 38A of the flying capacitor CFLY to an output node 42. The third charge pump switch SWCP3 may be adapted to selectively couple the second terminal 38B of the flying capacitor CFLY to ground. Finally, the fourth charge pump switch SWCP4 may be adapted to selectively couple the second terminal 38B of the flying capacitor CFLY to the supply voltage VSUPPLY. The clock generator 40 may be coupled to each one of the charge pump switches SWCP1-SWCPY and adapted to control the on or off state of each one of the charge pump switches SWCPI-SWCPY with one or more generated clock signals CLK.
In a charging phase, the first charge pump switch SWCP1 and the third charge pump switch SWCP3 are closed, while the second charge pump switch SWCP2 and the fourth charge pump switch SWCP4 are open, thereby connecting the flying capacitor CFLY between the supply voltage VSUPPLY and ground. Accordingly, the flying capacitor CFLY is charged to approximately the voltage of the supply voltage VSUPPLY. In a pumping phase, the second charge pump switch SWCP2 and the fourth charge pump switch SWCP4 are closed, while the first charge pump switch SWCP1 and the third charge pump switch SWCP3 are open, thereby connecting the flying capacitor CFLY in series between the supply voltage VSUPPLY and the output node 42. Accordingly, because the flying capacitor CFLY has been charged to approximately the supply voltage VSUPPLY, a voltage at the output node 42 is produced that is approximately double the supply voltage VSUPPLY. This process is continuously repeated in order to produce the bias voltage VBIAS.
The charge pump 36 in the bias control circuitry 26 may be a negative charge pump adapted to generate a negative biasing voltage VBIAS, a positive charge pump adapted to generate a positive biasing voltage VBIAS, or both. As is well known in the art, operation of the charge pump switches SWCP1-SWCPY produces noise in the form of signal spurs at or around the switching frequency of the charge pump 36 and harmonics thereof. Further, implementing the charge pump 36 in the bias control circuitry 26 increases the size of the bias control circuitry 26 and adds cost to the design and production of the bias control circuitry 26.
Accordingly, there is a need for transistor switching circuitry that is capable of maintaining an on or an off state without the need for a biasing power supply.